This invention relates generally to high power radio frequency (xe2x80x9cRFxe2x80x9d) amplifiers and association amplification methods utilized for radar, communications, and other applications and, in particular, to tube-type RF power amplifiers such as Klystron tubes and traveling wave tubes (xe2x80x9cTWTsxe2x80x9d) in which RF gain is provided by the interaction of an RF signal with a modulated beam of electrons in a vacuum tube.
For many radar and satellite communications applications, it is a common requirement to provide a radio frequency (xe2x80x9cRFxe2x80x9d) transmitter capable of delivering very high peak or average levels of RF power, such as to generate radar pulses in a radar application or to generate a high power continuous signal in a communications application. Although solid state approaches to transmitter amplifiers have been developed in recent years and are capable of producing ever-increasing levels of RF power output, many applications at higher RF frequencies for which high peak or average power levels are required dictate the use of a traveling wave tube (xe2x80x9cTWTxe2x80x9d) or Klystron tube-type amplifier.
A typical TWT or Klystron tube is an evacuated tube that includes at one end of the tube an electron beam source, such as an anode structure to which a high voltage is applied at an elevated temperature. The beam of electrons produced by the anode traverses the length of the tube structure and is collected by a collector located at the end of the tube opposite the anode. Because of the high flux of electrons through the tube, the collector element is typically large and bulky. In addition, a sizable heat sink is required to dissipate the large amount of heat created by the collection of the electrons.
In operation, an RF signal is introduced into the tube near the anode end. The RF signal interacts with the electron beam in a delay or xe2x80x9cslow wavexe2x80x9d structure inside the tube so as to be amplified considerably in the tube. By extracting the RF signal near the end of the tube, a high level of peak or continuous RF power can be delivered.
A traveling wave tube amplifier (xe2x80x9cTWTAxe2x80x9d) generally consists of a TWT plus an associated high voltage power supply. Within the tube structure, a TWT typically includes a slow wave structure that surrounds the electron beam and that extends in a lengthwise direction through the tube. By transmitting RF signals along the slow wave structure, the RF signals interact with the electron beam and are amplified in a continuous manner throughout the length of the slow wave structure. A TWT also generally includes a plurality of focusing magnets along the length of the tube, as well as an attenuator for reducing waves that would otherwise travel backward or upstream through the tube.
A Klystron tube also requires a high voltage power supply. In contrast to TWTs, a Klystron tube usually includes several discrete cavities in which the RF signals are amplified. Although the RF signals are carried between cavities by the electron beam, there is no coupling of the RF signals between the cavities such that the amplification of the RF signals is not continuous throughout the length of the tube.
In addition to the TWTs described above, coupled cavity TWTs have been designed that essentially include several tens of Klystron-like cavities that are electromagnetically coupled together so that RF signals can propagate therethrough. See A. S. Gilmour, Jr., Microwave Tubes, Artech House (1986) for a discussion on Klystron tubes and TWTs.
In many applications in which TWT and Klystron type tubes are deployed, such as satellite communications applications, it is often important to minimize the weight and size of transmitter hardware for a number of reasons. As a result of the size and weight of all the tube structures including the collector element, however, TWT and Klystron type tubes are inherently bulky and heavy, when compared to solid state alternatives, for example. As such, the weight and size of the collector in such a tube-based transmitter is often a significant portion of overall transmitter weight and size. The weight and size of the tube is often an important design driver for the radar system or the satellite transmitter as a whole. As a result, transmitter system designers have employed a number of techniques in an attempt to minimize weight and size. For example, U.S. Pat. No. 4,232,249 to Dietrich A. Alsberg proposes a TWT structure having a single anode or electron gun component for generating an electron beam that can be controllably deflected so as to travel through either one of two different delay structures for collection by different respective collectors, each of which may be thermally connected to a common collector heat sink.
In some radar or communications applications, high RF power levels must be generated at each of two or more distinct RF frequencies. For example, some communications systems operate at multiple frequencies, and some radar systems utilize multi-frequency transmitters to improved radar system performance. If the various transmitter frequencies in a multi-frequency system are sufficiently adjacent in frequency, a single TWT or Klystron tube may be employed to provide RF gain and power at all necessary frequencies. However, in some applications, the various transmitter frequencies are separated so widely in frequency that a common TWT or Klystron cannot be used. In those applications, multiple TWTs or Klystrons must be employed, each of which includes a relatively large and bulky collector element and high voltage power supply. As such, the resulting transmitter system will also be disadvantageously large and heavy which may limit the effectiveness of the transmitter system in weight-sensitive applications, such as in satellite or airborne hardware applications.
According to the present invention, an RF transmitter and an associated method are provided for producing a plurality of amplified output signals in response to a plurality of RF input signals. The RF transmitter of the present invention includes a plurality of RF tube sections. Each tube section defines an input and an output through which RF signals are introduced and extracted, respectively. Typically, each tube section amplifies RF signals having different frequencies, although RF signals of the same frequency can also be amplified. Each RF tube section includes an anode for producing an electron beam that passes through the tube section so as to amplify the RF signals. According to the present invention, the RF transmitter also includes a common collector for collecting each of the electron beams following propagation through the respective RF tube sections. In this regard, the common collector is preferably disposed proximate to the end of each RF tube section that is opposite the anode end to facilitate collection of each of the electron beams. By employing a common collector for each RF tube section, the weight and size of the RF transmitter is advantageously reduced relative to conventional RF transmitters having a plurality of tube sections with separate collectors for separately amplifying the different RF signals.
In addition to sharing the common collector, the RF transmitter can include a modulator that is shared by each of the RF tube sections for modulating each of the electron beams. In addition, the plurality of RF tube sections preferably cooperate to define a common vaccum tube, such as a Klystron tube or a traveling wave tube. The RF transmitter can also include a power supply for energizing the RF tube sections and a heat sink for dissipating heat generated in the common collector as electron beams are collected.
By utilizing common components, such as a common collector and, in some embodiments, a common modulator, the RF transmitter and associated method of the present invention permit a plurality of RF signals, each potentially having a different frequency, to be amplified by respective RF tube sections while still reducing the overall weight and size of the RF transmitter in comparison to conventional designs having a plurality of RF tube sections with separate components, i.e., separate collectors. Accordingly, the RF transmitter and associated method of the present invention are particularly advantageous for applications in which the cumulative weight and size are to be minimized, such as satellite communications and other airborne or space-related applications.